1. Northern Hemisphere
The 500-hPa height pattern during
February featured positive anomalies over the high latitudes of the central
North Pacific Ocean
, the polar region, the subtropical
North Atlantic Ocean
, and eastern
, and negative anomalies from eastern
, and across central and eastern
(Figs. E9, E11).
The main surface temperature departures reflected warmer-than-average
conditions across central and southern
, and the southern half of
, and cooler-than-average conditions across most of
and the northern half of
(Fig. E1). The main precipitation anomalies
included above-average totals across most of central and southern
, and below-average totals in the southeastern
, and northwestern
The middle- and upper-level
circulation during February featured an amplified trough over eastern
, and a mean ridge over western
(Fig. T22). This pattern was associated
with anomalously cold surface temperatures across
and the eastern half of the
, with departures in many areas averaging -2°C to -3°C (Fig. E1).
The most significant departures occurred in the upper-Midwest and
mid-Atlantic regions of the
, where mean temperatures were generally in the lowest 10th
percentile of occurrences.
the monthly temperature and precipitation patterns strongly reflected the
position of the mean upper-level ridge. Anomalously warm temperatures in
coincided with the ridge axis, and anomalously cool conditions in eastern
coincided with the area downstream of the ridge axis. Anomalous descending
motion and exceptionally dry conditions were observed across southern
within and immediately downstream of the mean ridge axis (Fig. E3).
The 500-hPa circulation during
February featured a 3-celled anomaly pattern with by positive height
and across the subtropical
, and negative height anomalies extending from the eastern
(Fig. E9). This pattern reflected the
combination of the negative phase (-0.5) of the North Atlantic Oscillation (NAO)
and the strong positive phase (+ 1.7) of the
teleconnection pattern (Table E1, Fig. E7).
These patterns contributed to cooler than average conditions across northern
, and warmer and wetter than average conditions across central and southern
A pronounced north-south
dipole pattern of 500-hPa height and surface temperature anomalies was
. Below-average heights and anomalously cool surface temperatures extended
across northern Russia and Siberia, with temperatures in many regions
averaging 2°C-3°C below normal and in the lowest 30th
percentile of occurrences. In contrast, surface temperatures were generally
3°-6°C above average across east-central
, in association with a persistent 500-hPa ridge centered just north of the
region. For central and eastern
, this is the second straight month with temperatures in the upper 10th
percentile of occurrences.
2. Southern Hemisphere
The 500-hPa circulation pattern during February featured
positive height anomalies in the area south of Australia and over the high
latitudes of the eastern South Pacific Ocean, and negative height anomalies
just downstream of southern South America (Fig. E15).
a persistent upper-level ridge in the west and trough in the east (Fig. T22)
contributed to extremely warm temperatures across the western half of the
continent, with many areas recording values in the upper 10th
percentile of occurrences (Fig. E1). This
anomalous circulation also contributed to well below-average precipitation
throughout the continent, with totals in the central and northwestern
regions falling in the lowest 10th percentile of occurrences (Fig.
rainy season extends from October to April. Precipitation during February
was below average, with the most significant departures observed in
where totals were in the lowest 10th percentile of occurrences.
So far during the 2006-07 rainy season, area-averaged totals were
below-normal in October and February, near-normal in November and December,
and above normal in January (Fig. E4).